Evaluation of creep rupture strength of high nitrogen ferritic heat-resistant steels using small punch creep testing technique

Abstract

The development of next generation ultra-heat-resistant ferritic steels for the future advanced thermal power plants which operate in excess of 700 o C are currently in progress in Japan. The small punch (SP) creep testing technique which uses miniature specimens has been applied to evaluate creep rupture strength of newly developed high nitrogen ferritic steels. The SP creep tests have been carried out on different grades of high nitrogen ferritic steels in the temperature range of 600-800 o C, under different loads in the range of 70-400 N, using specimens of dimension 8 mm x 0.5 mm. The SP creep rupture results of high nitrogen ferritic steels have been compared with that of conventional steel (Gr.91). The high nitrogen steels exhibited higher creep rupture strength when compared to the Gr.91. The creep rupture results obtained from SP creep tests were correlated to the uniaxial creep rupture results obtained from conventional creep tests using a stress conversion coefficient of. The paper investigates the applicability of SP creep testing technique for the evaluation of creep rupture strength of high nitrogen ferritic heat-resistant steels. .

Creep Properties Assessment by Shear Punch Creep Test and IMC Morphology of Aged Pb-Free Solder Joint/UBM

“…The Monkman-Grant relational equation is widely used in the creep failure modeling. It has also been used to evaluate this experiment to predict the creep rupture time [15]. This relationship is obtained from the relationship between the creep strain rate ( where, t r = fracture time, m = Monkman-Grant exponent, b = material constant.…”

Small Punch Creep

“…In a ductile failure, the fracture usually initiates around the periphery of the punch head in the vicinity of tensile membrane stretching, propagating along the circumference indicating that the maximum stress is found away from the central region of the disc. Figure 8 illustrates a typical example of a ductile fracture for a ruptured high nitrogenic ferritic steel specimen, tested at 725 C under a load of 140N [28]. The fracture morphology displays a cap-like form of deformation whilst severe necking can be seen around the central region of the disc.…”

“…A series of researchers [24,28] have applied the LMP to interpret SPC data, but to also establish a relationship between SPC and uniaxial creep results. Andrés et al [24] obtained a LMP design curve from SPC results on the magnesium alloy AZ31 through linear regression, once the equivalent uniaxial creep stress was defined.…”

“…(a) A typical SP creep ductile fracture surface for a test on HN9L at 725 C at 140N and (b) fracture surface depicting ductile transgranular mode of fracture[28].…”

Design and high temperature behavior of novel heat resistant steels strengthened by high density of stable nanoprecipitates

“…time to rupture or minimum creep rate. It has been employed satisfactorily to evaluate the creep strength of new alloys and welded joints in several works [29][30][31][32][33]. Furthermore, many works have been focused on extrapolating the creep results obtained by means of SPCT to conventional uniaxial creep tests and have highlighted the reliability of this miniaturized specimen testing technique to predict creep strength [34,35].…”